Fuel consumption for transportation accounts for a considerable portion of total U.S. energy consumption. The efficiency of conventional gasoline powered vehicles has been estimated at less than ten percent based on energy delivered to the drive train wheels [see Efficient Use of Energy, K. W. Ford, et al. (eds.), American Institute of Physics (New York 1975), p 99-121, which is incorporated herein by reference]. Vehicle efficiency is further reduced by mechanical energy losses dissipated as heat from braking, aerodynamic drag and road resistance. For urban driving conditions, it is estimated that as much as thirty percent of drive train energy is lost in vehicle braking and between thirty to fifty percent of drive train energy is lost to road resistance. It is estimated that the combination of road resistance and aerodynamic drag account for 20-30 kW of power for conventional passenger vehicles and as much as 125 kW of power for heavy trucks at moderate highway speeds. Through the introduction of innovative vehicle designs and technologies, fuel efficiency may be improved and mechanical energy losses recovered.
Energy efficiency in both electric and conventional gasoline powered vehicles is generally compromised by road resistance with associated parasitic energy losses caused by mechanical displacements produced by road bumps and road roughness. It is anticipated that a fifty percent reduction in road resistance could reduce fuel consumption by fifteen to twenty-five percent. Thus, innovative devices which can recover these energy losses with minimum vehicle weight penalty would be highly desirable for improving the overall energy efficiency of both conventional fossil fuel powered and electric powered vehicles.
Conventional vehicle shock absorbers and other suspension damping devices are known in the art. Isermann [IEEE/ASME Transactions on Mechatronics, v.1, no. 1, p.16-28 (March 1996)] has reviewed studies of semi-active vehicle suspension systems which are adaptive to changing vehicle conditions. While Isermann does not teach specific device designs or configurations, he discloses concepts of parameter adaptive vehicle suspension systems for continuously adjustable damping and feedback control for improved driving comfort and safety. Isermann does not appear to cite any references which teach or suggest a regenerative vehicle shock absorber which combines damping with power generation.
U.S. Pat. No. 3,842,753 to Theodore et al. discloses an improved damping system comprising an electro-magnetic damping means with feedback control means for dynamic control of undesirable vehicle suspension oscillations. Theodore does not appear to teach a means for generating power from suspension motion.
U.S. Pat. No. 4,815,575 to Murty discloses an electric, variable damping vehicle suspension device which converts vertical suspension motion into rotational motion which drives a multiphase alternator for generating electrical current flow through a variable load resistance. The load resistance and current are varied by a control signal sensitive to displacement motion to provide dynamic variation in vertical damping force. The disclosed device dissipates the suspension kinetic energy through a variable load resistance as heat and does not appear to teach or suggest energy recovery and power generation from suspension motion.
U.S. Pat. No. 3,941,402 to Yankowski, et al., discloses an electromagnetic shock absorber to supplement or replace conventional hydraulic vehicle shock absorbers for damping road vibrations. The disclosed device employs two electromagnets, one of which has fixed field produced by a unidirectional current flow and another whose polarity is reversible due to bi-directional current flow which is switched depending on the direction of the shock to be absorbed or dampened. The disclosed reversible field electromagnet can produce either a repulsive or attractive force with the fixed field magnet in response to undesirable movement of the vehicle frame. The disclosed device requires an external power source for energizing the electromagnets for damping. In another embodiment, Yankowski discloses the use of permanent magnets of fixed polarity where damping of shocks in only a single direction is required. Due to the pole to pole configuration employed and relatively low flux magnetic flux density produced, it is anticipated that the disclosed device provides for relatively weak damping by way of either repulsive or attractive forces acting between single poles of two adjacent electromagnets or magnets. The disclosed device consumes rather than generates power.
Linear motion generators which recover energy from repetitive linear motion or vibrational motion are also known in the art. Boldea, et al. [IEEE Int. Electric Machines and Drives Conf. Record, IEMDC 1997, IEEE (Piscataway, N.J.), p. MA1-1.1-MA1-1.5 (1997)], provide a review of the art of linear motors, actuators and generators as well as oscillating motors and generators that employ either moving coil stators, moving permanent magnet stators and moving iron stators. The disclosed devices generally have a cylindrical configuration and are typically designed to operating at fixed displacement frequency and fixed displacement amplitude. None of the disclosed devices appear to teach or suggest the use of linear generators as a shock absorber for damping.
U.S. Pat. No. 4,500,827 to Merritt, et al., discloses a linear reciprocating electrical generator with a reciprocating armature comprising a plurality of rectangular permanent magnets which are coupled to a source of relative motion. The device has applications in automotive suspension systems, windmills and in ocean wave power generation. In the disclosed embodiments, armature magnets are arranged with alternating magnetic poles, configured orthogonal to the direction of reciprocating motion, which oscillate within a fixed stator comprising a plurality of spaced windings. The magnetic poles of adjacent magnets are aligned with individual winding groups for inducing current. One limitation of the disclosed device is that it does not appear to fully utilize the magnetic field and flux created by the magnet array since the generator apparently exploits only single magnetic pole-coil interactions and does not appear to provide for positioning the coil windings in the region of maximum magnetic flux density. This limitation results in reduced efficiency and power generation capability. Merritt discloses alternative embodiments in which the generator armature is mechanically or hydraulically linked to a conventional automobile control arm and its shock springs.
U.S. Pat. No. 5,578,877 to Tiemann discloses a linear generator device for converting vibratory motion to electrical energy for powering tracking units, such as GPS or Loran-C receivers, or electronic sensors in vehicles such as railroad cars and tractor trailers. The disclosed device is apparently designed for large amplitude, low frequency motion where displacements are typically greater than one centimeter. In one disclosed embodiment, the apparatus comprises a carrier structure fitted with aligned rows of permanent rectangular magnets which are supported by a suspension means which allows reciprocating movement relative to an enclosure fitted with an armature assembly comprised of coil windings. In an alternative disclosed embodiment, the coil windings are attached to the vibrating carrier structure and the magnets are attached to the enclosure. The disclosed device does not appear to fully utilize the magnetic field and flux created by the magnet array since the magnet-coil configuration does not provide for placement of the coil windings in the region of maximum magnetic flux density. Since Tiemann teaches device enclosures made from ferromagnetic materials to couple to the magnets, the disclosed device will likely produce undesirable eddy currents within the housing enclosure during operation which will significantly dampen motion of the armature, resulting in reduced current output and compromised power generation capacity. It is anticipated that these limitations will result in a significant reduction in energy conversion efficiency and power generation capability. Tiemann discloses one embodiment where the generator is coupled to a charging circuit for recharging an attached battery. Tiemann does not appear to teach or suggest the use of the disclosed generator as a shock absorber.
U.S. Pat. No. 5,347,186 to Konotchick discloses several embodiments of a linear motion electric power generator which employ a cylindrical assembly of a rare earth NdFeB magnets and coil windings positioned to move reciprocally relative to each other. The device has applications in powering buoys, roadway signs, call boxes and portable radios. The disclosed device apparently is designed for relatively high amplitude, repetitive linear mechanical motion typically associated with high power motion such as ocean waves and jogging. One limitation of the disclosed embodiments is that they do not appear to fully utilize the magnetic field and magnetic flux generated from device magnets since the generator designs appear to exploit only single magnetic pole-coil interactions and do not appear to provide for positioning the coil windings in the region of maximum magnetic flux density. In one disclosed embodiment, Konotchick demonstrated a continuous power output of over 80 milliwatts could be maintained with hard shaking of the device. Konotchick also discloses circuitry for electrical regulation of the current and voltage output of the generator for charging batteries. In one preferred embodiment, the total power output observed by Konotchick's disclosed generator with intense shaking was limited to approximately 1 Watt or 1.54 watts per pound. The reported mechanical to electrical energy conversion efficiency for the total generator unit were relatively low, ranging from 2.7 to 4.8%. '186 to Konotchick does not appear to teach or suggest the use of his generators as shock absorbers.
U.S. Pat. No. 5,818,132 to Konotchick discloses alternative configurations of the cylindrical linear motion generator of '186 for converting low amplitude, low power, repetitive linear displacements, or intermittent linear displacements into electrical power. Disclosed applications for the device include power generation for flashlights, alarm systems and communication devices. The disclosed design is similar to the device of'186 to Konotchick except for the partial substitution of ceramic magnets, or magnetically permeable disks, in sandwiched layered structures with rare earth magnets to reduce cost. Additional disclosed embodiments include variations such as reversing coil winding direction in adjacent coils, connecting multiple generating units in parallel or increasing the number of moving magnets for increased power output, employing a vented tube configuration to avoid air damping of magnet travel, and enhancing generator sensitivity by orienting magnet travel vertically. One disclosed embodiment produced peak to peak voltage of 3 to 20 volts with mild to heavy shaking with 17.5 milliwatts of peak power. '132 to Konotchick does not appear to teach or suggest the use of the disclosed device as a regenerative shock absorber for vehicles.
Wang, et al. [IEEE Proc. Electric Power Applications, v145, no.6, p. 509-518 (November 1998)], disclose a small, linear microgenerator for generating low level electrical power as a battery substitute in telemetry vibration monitoring systems. The disclosed device employs rare earth NdFeB magnets in a translatable stator which vibrates within a cylindrical coil winding supported by beryllium copper springs to generate electrical power from the relative movement of the stator within the coil winding. The device requires springs with very high radial stiffness to withstand unbalanced magnetic forces and very low axial stiffness for operating at low resonance frequency. Wang's device is apparently designed for fixed vibrational frequencies and for stationary deployments. The device has a nominally 50 Hz fixed resonant frequency and a nominally ±0.8 mm fixed displacement stroke to provide an optimum power output. In one disclosed embodiment the device provides 11 milliwatts of power at about 4.3 Volts. Since the disclosed device apparently relies on natural resonance to drive the device with negligible damping provided, it is unlikely that the disclosed device could function as a shock absorber or provide acceptable power generation capacity and efficiency at the variable bump and displacement frequencies anticipated with vehicles under normal driving conditions on typical road surfaces.
U.S. Pat. No. 3,559,027 to Arsem discloses two embodiments of a regenerative vehicle shock absorber for converting mechanical energy into usable electric energy. In one electromechanical embodiment, the vertical motion of a vehicle wheel is converted to rotary motion with a threaded screw which causes a permanent magnet rotor to be rotated within a coil stator to create an alternating current which is converted to direct current by a rectifier for charging a battery. In an alternative electromagnetic embodiment, vertical wheel motion is directly employed to produce vertical movement of an magnet armature within a coil stator. In this embodiment, the armature is comprised of three coaxial permanent magnets mounted on a post which moves vertically within corresponding circular coil stators comprised of wire-wrapped, concentric, ring-shaped, iron cores to produce alternating current for charging a battery. The disclosed embodiments additionally employ a concentric steel shell housing which surround the magnets and stators. In one disclosed embodiment, resistance may be introduced in a control circuit as desired to vary the stiffness of the shock absorber.
Arsem's device apparently suffers several design limitations which compromise its performance. By employing wire-wound, concentric iron cores in the stators and steel housings, it is anticipated that movement of the magnets within the coil windings and housing would generate significant circumferential eddy currents within the magnetically permeable iron cores and housing which would produce equal and opposing magnetic fields to that of the magnets. This is due to the well-known principle stated in Lenz' law, that the induced current in the iron core loop will always flow in a direction such that the magnetic field induced by the current in the loop opposes motion. Thus, the resultant opposing magnetic field of nearly equal magnitude induced in the iron stator cores and steel housing would substantially dampen any vertical or rotary motion of the magnet armature within the coil stator due to attractive forces between the permanent magnets and the induced magnetic fields in the iron stator cores and housing.
In addition, the volume occupied by the iron cores within Arsem's stators substantially reduces both the coil volume and magnetic flux density available to the actual stator coil winding further limiting coil output current and electric power generating capacity. Furthermore, according to Faraday's law, vertical displacement of the magnet armature within the coil stator, will induce a current flowing in a circumferential direction. Since, as shown in FIG. 4 of '027 to Arsem, the predominant portion of the stator coil windings are wrapped around the iron stator cores in a direction perpendicular to the circumferential direction of the induced current flow, most of the coil stator winding volume is wasted since the perpendicularly oriented winding generates essentially no induced circumferential current while substantially increasing coil resistance due to the excessive length of inactive winding, thereby creating undesirable electric power losses due to the substantial joule heating energy losses.
Mechanical, hydraulic and electromechanical devices for recovering energy from the mechanical displacement of vehicle suspensions are also known in the art. U.S. Pat. No. 3,861,487 to Gill discloses a mechanical device for converting vehicle vertical displacements to rotary motion for driving vehicle electrical components. The disclosed embodiments comprise variations of rack and pinion gears, pulleys, belts and drive shafts to convert reciprocating linear motion into rotary motion for driving alternators or generators to charge vehicle batteries.
U.S. Pat. No. 3,921,746 to Lewus discloses an auxiliary hydraulic power system for vehicles which converts vertical suspension motion to rotary motion for driving an electrical generator. A series of rack and pinion gears, levers, pistons, and pumps are employed, with hydraulic pumps, conduits and motors, for converting kinetic energy into electrical energy for operating auxiliary equipment. The disclosed device allegedly has sufficient inertia or mechanical resistance to suppress vertical movement and provide for shock absorption.
U.S. Pat. No. 3,981,204 to Starbard discloses a mechanical device for converting vertical reciprocating motion of a vehicle suspension to rotary motion for driving electrical alternators through a series of rack and pinion gears, pulleys, belts and drive shafts. The gears and belts allegedly provide sufficient drag to produce a shock absorbing effect.
U.S. Pat. No. 4,032,829 to Schenavar discloses a mechanical device which employs rack and pinion gears, drive shafts, springs, flywheels and clutches for transforming reciprocating vehicle axle motion to rotary motion for driving an electrical generator.
U.S. Pat. No. 4,387,781 to Ezell et al. disclose a mechanical device comprising a pair of opposing rotary electrical generators driven by a rack and pinion system of gears, shafts and springs for converted wasted vehicle kinetic energy from reciprocating vertical wheel movement into rotary movement for driving generators to produce useful electrical energy.
U.S. Pat. No. 5,036,934 to Nishina, et al. discloses a mechanical device comprising gears, shafts and levers for converting vertical vehicle axle movement into rotary motion for driving a magneto generator to produce electrical current to recharge a vehicle battery.
Conventional mechanical devices which attempt to convert suspension displacements from road vibrations and bumps into useful electrical energy suffer from a number of limitations. Mechanical devices which convert vertical motion into rotary motion for driving conventional generators or alternators typically employ a complex series of rack and pinion gears, levers, clutches, shafts, springs and drive belts which typically have a high weight and space penalty, high mechanical inertia, high displacement response threshold, slow displacement response time, large hysteresis due to requisite mechanical tolerances, and significant energy conversion losses due to heat generated from mechanical friction between components. Such conventional mechanical motion conversion devices are typically unresponsive to the high frequency, low amplitude bumps and vibrations which are a predominant source of road surface roughness and vertical wheel displacements under typical driving conditions. These mechanical devices generally require much larger vertical displacements at lower frequencies than are typically encountered in normal driving conditions. Thus, such devices would generally provide relatively low average power generation capability and efficiency under typical urban or highway driving conditions.
While electromagnetic devices which convert reciprocal linear motion into electrical energy, such as the devices disclosed in '827 to Merrit, et al., '877 to Tiemann, '186 and '132 to Konotchick and '027 to Arsem, do not suffer from the same limitations as conventional mechanical motion conversion devices, the power generating capacity, efficiency and energy conversion characteristics of such electromagnetic devices are critically dependent on proper magnet and coil configuration and orientation with respect to displacement motion. The performance of these prior art devices is generally compromised by non-optimized magnet and coil placement and magnetic pole orientations, excessive magnet-coil air gaps, underutilized coil volume, excessive coil resistance, unproductive coil winding orientation, a lack of overlap and combination of magnetic fields from multiple magnets for increased magnetic flux density, reduced magnetic flux density within the coil volume, a lack of accommodation for variable frequency operation to exploit realistic displacement frequencies and amplitudes, inadequate damping and poor matching of device current and voltage output to external electrical power requirements. Thus, conventional regenerative electromagnetic generator devices do not currently provide for efficient and viable power generation and damping for actual displacements and vibrations encountered under normal driving conditions on typical road surfaces.
Due to the limitations of current linear motion energy generator devices, it would be advantageous to provide an efficient, variable frequency, regenerative, linear electromagnetic generator with high power generating capacity and high energy conversion efficiency. Due to limitations in power generation capabilities and energy conversion efficiencies of conventional linear electromagnetic generator, electromagnetic generators which have a high power to weight and high power to volume ratio would be particularly useful in portable generator or regenerative electromagnetic vehicle shock absorber applications to justify the additional cost and weight penalty of such auxiliary power generating devices. For example, the linear electromagnetic generator devices disclosed in '186 and '132 to Konotchick exhibit peak power outputs ranging from 100 microwatts to 90 milliwatts at between 3 to 20 volts, a measured 2.7-4.8% energy conversion efficiency, and an apparent maximum power generating capacity of 1 to 1.54 watts per pound when the disclosed devices are subjected to vigorous displacement motion. It is unlikely that generator devices having such low power output, power generation capacity and energy conversion efficiency would be suitable for vehicle applications where estimates of road rolling resistance losses for typical passenger vehicles traveling between 40 mph and 60 mph on typical road surfaces range from about 3 kW to 10 kW, representing between 30 to 50% of the typical power and total energy delivered to vehicle power trains [see Efficient Use of Energy, Part I, A Physics Perspective, K. W. Ford, et al. (eds.), American Institute of Physics (New York 1975) p 99-121].
To achieve optimum vehicle fuel efficiency with auxiliary power generating devices which recuperate energy losses from parasitic displacement motion from road bumps and vibrations, it would be advantageous to develop innovative regenerative devices which exhibit high energy conversion efficiency and power generation capacity and supplement vehicle power requirements for vehicles traveling at normal speeds on typical road surfaces. Due to the potential power generation capabilities and energy conversion efficiencies of linear electromagnetic generator devices when compared to conventional mechanical linear motion conversion devices, regenerative electromagnetic shock absorbers whose electrical output characteristics are matched to vehicle power, damping and electrical load requirements for typical driving conditions are prime candidates for improving vehicle fuel efficiency. Devices which can operate at typical road bump frequencies, ranging from 1/10 to 1/100 cm−1, and typical road bump amplitudes, ranging from 1 to 6 mm, and which satisfy vehicle electrical system requirements are particularly useful. In order to justify the additional cost and weight penalties for equipping vehicles with these auxiliary power generation devices, regenerative devices which are capable of generating peak power ranging between 2 to 20 kW, average power ranging from 1 to 6 kW, with a power generation capacity ranging between 10 to 100 watts per pound, with typical energy conversion efficiencies of at least 50% would be most advantageous. Additionally, a regenerative vehicle shock absorber which provides not only efficient energy recovery but also road shock and vibration damping are particularly desirable for satisfying the competing requirements of increased fuel efficiency and enhanced passenger comfort and safety.